Identification of the primary mechanism of complement evasion by the periodontal pathogen, Treponema denticola

Abstract

SUMMARYTreponema denticola, a periodontal pathogen, binds the complement regulatory protein, Factor H (FH). FhbB (FH binding protein B) is the sole FH binding protein produced by T.denticola. The interaction of FhbB with FH is unique in that FH is bound to the cell and then cleaved by the T.denticola protease, dentilisin. A ~50kDa product generated by dentilisin cleavage is retained at the cell surface. Until this study, a direct role for the FhbB-FH interaction in complement evasion and serum sensitivity has not been demonstrated. Here we assess the serum resistance of T.denticola strain 35405 (Td35405wt) and isogeneic mutants deficient in dentilisin (Td35405-CCE) and FhbB production (Td35405)fhbB), respectively. Both dentilisin and FhbB have been postulated to be key virulence factors that mediate complement evasion. Consistent with conditions in the sub-gingival crevice, an environment with a significant concentration of complement, Td35405wt was resistant to serum concentrations as high as 25%. Deletion of fhbB (Td35405)fhbB), which resulted in the complete loss of FH binding ability, but not inactivation of dentilisin activity (Td35405-CCE), rendered T.denticola highly sensitive to 25% human serum with 80% of the cells being disrupted after 4 hours of incubation. Heat treatment of the serum to inactivate complement confirmed that killing was mediated by complement. These results indicate that the FH-FhbB interaction is required for serum resistance while dentilisin is not. This report provides new insight into the novel complement evasion mechanisms of T. denticola.

Structure of Factor H-binding Protein B (FhbB) of the Periopathogen, Treponema denticola

“…FhbB is the smallest (11.4 kDa) bacterially produced FH-binding protein identified to date (20,21). FhbB binds and positions FH on the cell surface thus allowing FH cleavage by the T. denticola protease, dentilisin (22)(23)(24). It is our hypothesis that in vivo, FH cleavage leads to its depletion in the subgingival crevice resulting in local dysregulation of complement and conditions that favor the development and progression of periodontal disease.…”

The Surface Layer of Tannerella forsythia Contributes to Serum Resistance and Oral Bacterial Coaggregation

“…Inhibition of C3b deposition by recruiting the complement-controlling protein factor H or C4BP contributes to serum resistance (30,32,33). Factor H inhibits the alternative pathway in complement activation, while C4BP inhibits the classical and lectin pathways.…”

“…The mechanism of complement resistance in bacteria functions through three main pathways: protease digestion of complement components; recruitment of factors such as factor H and C4BP, which inhibit complement activation, to the bacterial cell surface; and polysaccharide-mediated suppression of complement activation (16,(30)(31)(32)(33). In periodontal bacteria, P. gingivalis possesses all three resistance systems.…”

“…Bacterial components such as lipopolysaccharides (LPS), peptidoglycan, and lipoproteins can induce complement activation. However, many bacteria, including periodontal pathogens, are resistant to human serum (16,(30)(31)(32)(33). Coaggregation between different bacteria plays a key role in the colonization of the gingival crevice and the organization of biofilm formation by periodontal pathogens.…”

The Antibacterial Activity of LL-37 against Treponema denticola Is Dentilisin Protease Independent and Facilitated by the Major Outer Sheath Protein Virulence Factor

“…These include motility, the ability to attach to host tissues (21), coaggregation with other oral bacteria (41,62), complement evasion mechanisms (53), and the presence of several outer sheath and periplasmic proteolytic and peptidolytic activities (47,63,64). The proteolytic capacity of T. denticola sustains its nutritional requirements (69) and ATP production (65,68).…”